The present invention relates to an apparatus for inspecting a surface of a web material continuously moving lengthwise by scanning the surface in the direction of the width of the web material with a light beam so as to detect surface defects of the web material.
Various apparatus are well known for scanning a surface of a continuously running web material, such as films, paper sheets, thin plates or the like, with a scanning beam in the direction of the width of the web material to detect surface defects of the web material. Some of these surface scanning apparatus utilize a photoelectric light detector which is adapted to receive light modulated by surface defects to provide defect signals. Based on the defect signals a judgment is made as to whether the web material has unacceptable surface defects. Because they are non-contact devices and permit high speed surface defect detection, these surface inspection apparatus can be used in a web material production line.
One such surface inspection apparatus of the type utilizing a scanning beam and a photoelectric light detector is disclosed in Japanese Patent Publ. No. 56-39,419. The surface inspection apparatus disclosed therein is adapted to store data as to the surface defects of a web material and the positions of the surface defects in memories or shift registers every transverse scan. After the storage of the data for several transverse scans, the web material is evaluated based on these data by the aid of a computerized evaluation system.
A problem with such surface inspection apparatus is that the efficiency of inspection depends on the memory capacity because data on surface defects are memorized in the memory every transverse scan. For example, if the surface inspection apparatus can scan a web material in the direction of the width of the web material about 3,000 times per second, 3,000 memories can memorize only the data obtained for one second. Therefore, when inspecting the web material running at a speed of 60 m/min, data on surface defects only for one meter of the web material can be memorized in the 3,000 memories. On the other hand, if the web material to be inspected by the surface inspection apparatus runs at a slow speed of movement, a considerably greater number of memories are needed to memorize data on surface defects for a predetermined length of the web material.